[client] Add reverse dns zone

[lixmal]

Describe your changes

Issue ticket number and link

Closes #3214

Checklist

• Is it a bug fix
• Is a typo/documentation fix
• Is a feature enhancement
• It is a refactor
• Created tests that fail without the change (if possible)
• Extended the README / documentation, if necessary

[mlsmaycon]

are we adding the PTR zone as search domain?

[lixmal]

are we adding the PTR zone as search domain?

I've excluded it but seems it's not marked by OS tools anyway

[hakansa]

we can split the logic to make it more readable

func addReverseZone(config *nbdns.Config, ipNet *net.IPNet) {
	zoneName, err := reverseZoneName(ipNet)
	if err != nil {
		log.Warn(err)
		return
	}

	if zoneExists(config, zoneName) {
		log.Debugf("reverse DNS zone %s already exists", zoneName)
		return
	}

	records := collectPTRRecords(config.CustomZones, ipNet)
	config.CustomZones = append(config.CustomZones, nbdns.CustomZone{
		Domain:  zoneName,
		Records: records,
	})

	log.Debugf("added reverse DNS zone: %s with %d records", zoneName, len(records))
}

// reverseZoneName computes the reverse DNS zone name
func reverseZoneName(ipNet *net.IPNet) (string, error) {
	networkIP := ipNet.IP.Mask(ipNet.Mask)
	maskOnes, _ := ipNet.Mask.Size()
	// round up to nearest byte
	octetsToUse := (maskOnes + 7) / 8

	octets := strings.Split(ip4.String(), ".")
	if octetsToUse > len(octets) {
		return "", fmt.Errorf("invalid network mask size for reverse DNS: %d", maskOnes)
	}

	// reverse the first octetsToUse octets.
	reversed := make([]string, octetsToUse)
	for i := 0; i < octetsToUse; i++ {
		reversed[octetsToUse-1-i] = octets[i]
	}

	zone := fmt.Sprintf("%s.in-addr.arpa", strings.Join(reversed, "."))
	return dns.Fqdn(zone), nil
}

// zoneExists returns true if the given zone name already exists in the configuration.
func zoneExists(config *nbdns.Config, zoneName string) bool {
	for _, zone := range config.CustomZones {
		if zone.Domain == zoneName {
			return true
		}
	}
	return false
}

// collectPTRRecords iterates over all A records in the existing zones,
// creating PTR records where applicable.
func collectPTRRecords(zones []nbdns.CustomZone, ipNet *net.IPNet) []nbdns.SimpleRecord {
	var records []nbdns.SimpleRecord
	for _, zone := range zones {
		for _, record := range zone.Records {
			if record.Type != int(dns.TypeA) {
				continue
			}
			if ptrRecord, ok := createPTRRecord(record, ipNet); ok {
				records = append(records, ptrRecord)
			}
		}
	}
	return records
}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud